Prefabricated modular flooring and roofing system

ABSTRACT

A plurality of elongated precast concrete beams or slabs are prestressed longitudinally and arranged in parallel relation to form a waffle-type floor structure. Each of the beams or slabs includes a plurality of longitudinally spaced and laterally extending integral walls through which reinforcing tubes define corresponding openings. The openings in each beam or slab align with corresponding openings in each adjacent beam or slab, and a cable extends through each series of aligned openings. Each cable is post-tensioned and is then attached by cement mortar to the corresponding tubes to provide a modular floor or roof structure which distributes loads generally uniform in all directions. In one embodiment, a series of T-shaped and/or L-shaped precast reinforced slab members may be positioned between each set of adjacent beams and are adapted to rest on bosses projecting outwardly from the opposing sides of the adjacent beams. The slab members have reinforcing tubes defining openings which align with the openings within the beams and which also receive the cables before they are tensioned and cemented to the tubes. In another embodiment, the slabs are supported by a framework of prestressed elongated beams, and the ends of each beam are supported by precast head members mounted on the top of upright columns. The laterally extending post-tensioned cables are attached to loops projecting upwardly from the adjacent beams, and a layer of topping concrete covers the loops and cables on each beam.

Bahramian [451 Nov. 11, 1975 PREFABRICATED MODULAR FLOORING AND ROOFING SYSTEM [76] Inventor: Bahram Bahramian, PO. Box

7 15/1114, Tehran, Iran [22] Filed: June 3, 1974 [21] Appl. No.: 475,430

[52] US. Cl. 52/227; 52/745; 29/452; 52/263; 52/301 [51] Int. Cl. E04G 21/00; E04C 3/10; B21D 39/00 [58] Field of Search 52/251, 252, 253, 263,

[56] References Cited UNITED STATES PATENTS 707,924 8/1902 Hennebique 52/690 915,421 3/1909 Eisen 52/252 938,458 11/1909 Brockhausen 52/283 961,683 6/1910 Conzelman 52/252 1,376,152 4/1921 Moore 52/259 1,385,606 7/1921 Christensen 52/227 1,516,074 ll/l924 Borg 52/252 2,374,624 4/1945 Schwendt 52/301 2,618,146 11/1952 Ciarlino 52/236 2,677,957 5/1954 Upson 52/230 3,152,421 10/1964 Middendorf 52/223 R 3,495,367 2/1970 Kobayashi 52/602 3,495,371 2/1970 Mitchell 52/236 3,567,816 3/1971 Embree 52/602 FOREIGN PATENTS OR APPLICATIONS 711,449 6/1954 United Kingdom 52/227 1,215,626 12/1970 United Kingdom 52/234 854,940 1l/l970 Canada 52/263 1,450,491 7/1966 France 52/126 Primary E.\'aminer.lames L. Ridgill, Jr. Attorney, Agent, or Firm-Jacox & Meckstroth [57] ABSTRACT A plurality of elongated precast concrete beams or slabs are prestressed longitudinally and arranged in parallel relation to form a waffle-type floor structure. Each of the beams or slabs includes a plurality of longitudinally spaced and laterally extending integral walls through which reinforcing tubes define corresponding openings. The openings in each beam or slab align with corresponding openings in each adjacent beam or slab, and a cable extends through each series of aligned openings. Each cable is post-tensioned and is then attached by cement mortar to the correspond ing tubes to provide a modular floor or roof structure which distributes loads generally uniform in all directions. In one embodiment, a series of T-shaped and/or L-shaped precast reinforced slab members may be positioned between each set of adjacent beams and are adapted to rest on bosses projecting outwardly from the opposing sides of the adjacent beams. The slab members have reinforcing tubes defining openings which align with the openings within the beams and which also receive the cables before they are tensioned and cemented to the tubes. In another embodiment, the slabs are supported by a framework of prestressed elongated beams, and the ends of each beam are supported by precast head members mounted on the top of upright columns. The laterally extending post-tensioned cables are attached to loops projecting upwardly from the adjacent beams, and a layer of topping concrete covers the loops and cables on each beam.

4 Claims, 12 Drawing Figures US. Patent Nov. 11,1975 Sheet 10f2 3,918,222

lmxx avggga US. Patent Nov. 11, 1975 Sheet 2 of2 3,918,222

PREFABRICATED MODULAR FLOORING AND ROOFING SYSTEM BACKGROUND OF THE INVENTION In the construction of a concrete floor or roof for a building structure. it is common to use a plurality of elongated precast and prestressed concrete modules or beams which are positioned in side-by-side parallel relation on a steel frame or support structure. This modular floor or roof assembly eliminates the need for erect ing forms and pouring .or casting a concrete floor at the building site. However, the weight of each of these concrete modules or beams is supported entirely by one set of opposite sides of the frame on which the end portions of the beam rest. The same side of the frame must also support the load on each beam since the load distribution by each beam is only in one direction which is longitudinally of the beam.

When it is desirable for the weight of a floor or roof structure and the load supported thereby, to be distributed substantially uniformly to the four sides of the frame structure, that is, a two-directional distribution of the load. it is common to erect a set of forms and to cast a concrete floor or roof which has both laterally and longitudinally extending reinforcing beams. When the forms are removed, the crossing beams form a waffle-like appearance from the underneath side of the floor or roof. However, it has been found that the erecting of the forms and the casting of a reinforced concrete floor having a waffle-like bottom surface, requires substantially more time and labor than does the assembly of precast and prestressed concrete modular beams on the supporting frame of the building structure.

SUMMARY OF THE INVENTION The present invention is directed to an improved prefabricated modular flooring or roofing system and a method for producing the same. The flooring and roofing system of the invention provides for a substantially uniform distribution of the weight of each floor or roof and the load supported thereby to the frame or walls extending around the periphery of the floor or roof. That is, the modular floor and roof system of the invention provides for a two-way or X-Y distribution of the load to the four walls bordering the floor or roof. As another important feature, the roof and floor system of the invention eliminated the need for erecting forms and provides for a simplified and rapid construction of the floor or roof.

In accordance with one of the illustrated embodiments of the invention, a plurality of precast elongated concrete beams are positioned in parallel relation on an outer supporting frame structure. Each of the beams is reinforced by longitudinally extending reinforcing rods and/or prestressed cables which are connected by laterally extending reinforcement tubes. The reinforcing tubes extend laterally through corresponding longitudinally spaced intermediate walls of each beam member, and the openings defined by the tube of each beam aligned with a corresponding opening within each adjacent beam. I g Y A steel cable extends through each series of aligned openings within the beams and are tensioned and cemented to the corresponding reinforcing tubes to provide a floor or roof structure which is reinforced or prestressed in the longitudinal direction of the beams and 2 is post-tensioned in a direction normal to the parallel beams. The sides of the precast modular beams are formed with outwardly projecting bosses for supporting intermediately spaced precast concrete slabs which are also reinforced by tubes defining openings for receiving the cables.

In another embodiment, each precast floor slab has a waffle-type configuration. and a plurality of the slabs are supported in parallel adjacent relation by a frame formed of precast beams. The ends of the beams are supported by precast head members which mount on corresponding support columns, and the post-tension cables are connected to the corresponding beams by a topping layer of concrete poured onto the beams.

Other features and advantages of the invention will be apparent from the following description. the accompanying drawing and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a fragmentary perspective view of a completed concrete floor constructed in accordance with the present invention;

FIG. 2 is a fragmentary bottom view of the floor shown in FIG. 1;

FIG. 3 is a fragmentary perspective view of the floor shown in FIGS. 1 and 2 and with some of the components or elements illustrated in exploded positions before assembly;

' FIG. 4 is a fragmentary perspective view of a reinforcing structurefor one of the precast concrete beams shown in FIG. 3;

FIG. 5 is a slightly enlarged fragmentary section taken generally on the line 55 of FIG. 3;

FIG. 6 is a fragmentary section taken generally on the line 6-6 of FIG. 5;

FIG. 7 is a slightly enlarged fragmentary section taken generally on the line 77 of FIG. 3;

FIG. 8 is an enlarged fragmentary section of a portion of a precast modular element shown in FIG. 6;

FIG. 9 is a fragmentary section of two adjacent beams constructed and assembled in accordance with another embodiment of the invention;

FIG. 10 is a fragmentary perspective view of a floor system constructed in accordance with another embodiment of the invention;

FIG. 11 is an exploded perspective view of a portion of the system shown in FIG. 10; and

FIG. 12 is an enlarged fragmentary vertical section of the floor system shown in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A floor structure or system 15 constructed in accordance with the present invention, is shown in FIGS. 1 and 2, and has the general appearance of a cast-inplace concrete floor having a waffle-like bottom appearance as mentioned above. This floor structure is constructed by positioning a plurality of parallel spaced elongated modular slabs or beams 18 on a pre-ereeted frame structure (not shown) consisting of a series of vertical frame members or columns rigidly connected by horizontal frame members or cross-beams. Each of the slabs or beams 18 is prefabricated or precast from a concrete material and includes a pair of longitudinally extending sidewalls 22 integrally connected by an upper or top wall 24 and a plurality of longitudinally spaced and laterally extending intermediate walls 26. These walls cooperate to define a plurality of longitudi- 3 nally spaced open bottom cavities 28 within each of the beams 18.

As shown in FIGS. 3 and 5, each of the sidewalls 22 of each beam 18 includes a series of longitudinally spaced and outwardly projecting bosses 31 which are cast as an integral part of the beam. The bosses 31 define a corresponding series of longitudinally spaced slots or grooves 32 between the ends of the bosses 31. Each boss 31 has a benerally triangular configuration and forms a longitudinally extending surface or seat 33 along the top of each boss. That is. the outer surface of each boss 31 tapers inwardly toward the bottom of the beam I8, and the inner surface of each groove 32 ta pers inwardly toward the top surface of the beam 18.

The inner surfaces of the sidewalls 22 and the intermediate walls 26 also taper outwardly towards the top wall 24 of the beam I8 so that the cavities 28 each have a truncated pyramid configuration. These tapered wall surfaces provide for convenient removal of each beam 18 from its corresponding mold after the concrete has set. As shown in FIG. 5, a tube section 36 extends through each of the intermediate walls 26 of each beam 18 and is positioned within the mold prior to casting the beam 18 to provide for extending electrical and fluid lines within the floor structure after it is assembled. Preferably tube sections 36 are formed from steel tubing.

Referring to FIGS. 3 and 4, each of the beams 18 is reinforced by a steel reinforcing structure 38 (FIG. 4) which includes a series of longitudinally extending parallel reinforcing rods 39 rigidly connected by spot welds to a plurality of sets of vertical reinforcing rods 41 and a plurality of longitudinally spaced sets of laterally extending upper and lower steel reinforcing tubes 42. Each of the tubes 42 has a square cross-sectional configuration and defines a correspondingly shaped passage or opening 44 extending through the tube. As shown in FIG. 5, each set of upper and lower tubes 42 extends laterally through the corresponding intermediate wall 26 of the beam 18, and the ends of the passages or openings 44 open into the corresponding grooves 32 defined between the ends of the outwardly projecting bosses 31 on each beam 18.

As shown in FIGS. 3 and 6, a series of modular elements or slab members 46 and 48 are positioned between each pair of adjacent beams 18 and are precast of a reinforced concrete material either in the same manner as the beams 18 or in a continuous manner with insert dividers forming the ends of each of a slab member. Each of the slab members 46 includes an upper or top wall 51 which is integrally formed with a center vertical wall 52 to define a generally T-shaped cross-sectional configuration. Each of the slab members 48 includes a top wall 54 and one sidewall 56 to define a generally inverted L-shaped configuration. The slab members 46 and 48 are each reinforced by a steel reinforcing structure which includes a corresponding set of upper and lower steel reinforcing tubes 42 defining corresponding passages or openings 44 extending longitudinally through the slab member.

The slab elements or members 46 and 48 are positioned between each pair of adjacent beams 18 so that the ends of the upper walls 51 and 54 of the slab members rest upon the corresponding seats 33 defined by the bosses 31 on the beams 18. The ends of the vertical walls 52 and 56 interfit into the corresponding grooves 32 defined between the bosses 31, and the upper fiat surfaces of the slab members are flush with the upper flat surfaces of the beam 18. After the slab members 46 and 48 are assembled in this manner. the openings 44 defined by the reinforcing tubes 42 within the slab members 46 and 48 align with the corresponding openings 44 defined by the laterally extending reinforcing tubes 42 within the beams 18 so that the upper and lower sets of aligned openings extend across the entire width of the floor structure. As shown in FIG. 6, the vertical walls 52 and 56 of the slab members 46 and 48 respectively. cooperate with the side walls 22 of the adjacent beams 18 to define corresponding cavities 28. In addition each wall 52 and 56 is provided with a tube section 36 to provide for conveniently extending electrical and fluid lines within the floor structure.

After the precast beams 18 and slab members 46 and 48 are assembled on the support frame structure (not shown). an elongated reinforcing member or steel cable 60 (FIG. 8) is extended through at least each series of the lower aligned openings 44 within the beams 18 and the slab members 46 and 48. Preferably. the leading end of each cable 60 is provided with a slip-on plastic fitting (not shown) having a pointed end surface which simplifies threading or pushing each cable 60 through the aligned series of openings 44. If a portion of the assembled floor structure is supported in a cantilevered manner. cables 60 are also extended through the upper set of openings 44 within the beams and slab members to provide for the change in bending m0- ments resulting from the cantilevered portion.

Clamps (not shown) are secured to the end portions of each cable 60 projecting outwardly from the opposite sides of the floor structure, and the cables are tensioned by hydraulic jacks. The reinforcing tubes defining the openings 44 are then pumped full or filled with a grout or cement mixture 62 which is allowed to set and cure for bonding or securing each of the cables 62 to the corresponding set of aligned reinforcing tubes. After this tensioning operation with the cables 60, and the setting of the cement mixture 62, the entire floor structure is reinforced or post-tensioned in a laterally extending direction to provide for a two-way distribution of the weight of the floor structure and the load supported by the floor structure to the supporting frame structure extending adjacent the four sides of the floor.

Referring to FIG. 9 which shows a modification of a floor or roof structure constructed in accordance with the invention, a series of elongated beam members 68 are precast or prefabricated in a manner substantially the same as the beams 18 and with reinforcing structure 38 such as shown in FIG. 4. However, instead of being placed in parallel spaced relation as shown in FIG. 3 for receiving the intermediate slab members 46 and 48, the beams 68 are positioned in parallel continuous relation so that the slab members 46 and 48 are eliminated. Each of the beams 68 includes longitudinally extending opposite side walls 69 and 72 which are integrally connected by an upper wall 74 and a series of longitudinally spaced and laterally extending intermediate walls 76. The side walls 69 and 72, the top wall 74 and the intermediate walls 76 of each beam 68 cooperate to define a corresponding series of longitudinally spaced open bottom cavities 78 each having a generally truncated pyramid configuration similar to the configuration of the cavities 28 within the beams 18.

The sidewall 72 of each of the beams 68 includes an outwardly projecting integral bottom lip or flange por' tion 79 which forms a seat for receiving the bottom of the somewhat shorter sidewall 69 of the adjacent beam 68 (FIG. 9). The laterally extending reinforcing tubes 42 within each of the beams 68 align with the corresponding tubes 42 within each adjacent beam 68 so that each series of correspondingly aligned openings 44 are adapted to receive a reinforcing cable 60 in the same manner as described above in connection with the beams 18. Each laterally extending reinforcing cable 60 is tensioned and cemented or secured to the corresponding reinforcing tubes 42 to provide a floor structure which is reinforced longitudinally and laterally post-tensioned in, the same manner as the floor structure shown in FIGS. 3 7.

Referring to FIGS. 12 which show another modular form of roof or floor system constructed in accordance with the invention. a set of precast concrete panels or slabs 90 each have a rectangular configuration and are arranged in side-by-side relation to form a complete rectangular bay. Each of the slabs 90, which by itself is not a complete flooring slab and it is only apart or segment of it. includes a plurality of longitudinally extending walls 90 which are integrally connected by laterally extending walls 94 and a top wall 96 to define a plurality of rows of downwardly facing cavities each having a square or rectangular configuration to form a waffle-type construction. Each of the walls 92 and 94 have a tapered configuration as shown in FIG. 12, and elongated prestressed rods or cables 99 (FIG. 12) ex tend longitudinally of the slabs 90 through the lower portion of each longitudinally extending wall 92. A series of longitudinally spaced tubes 101 extend laterally through the walls 94 and are secured to the prestressed or reinforcing members 99, for example, by spot welds. The tubes 101 within the end slabs 90 of each set, have end portions which curve upwardly adjacent the outer side walls 92 of the slabs, and the ends of each tube 101 terminate within corresponding cavities 103 formed within the outer longitudinal walls 92.

The opposite ends of each precast concrete slab 90 are supported by corresponding elongated precast con crete beams 105 each of which includes outwardly projecting and longitudinally extending flange portions 106 adjacent the bottom of each beam. The outer longitudinal edges of the end slabs 90 within each bay. are supported by corresponding elongated precast concrete beams 110 each of which also includes longitudinally extending bottom flange portions 111. Each of the beams 105 and 110 is prestressed by longitudinally extending members 112 in the form of prestressed rods or cables which are located within the upper and lower portions of the beam. The precast concrete beams 110 include a series of longitudinally spaced inverted U- shaped loop members 114 each of which has a lower portion embedded in the concrete beam 110.

Each of the precast and prestressed beams I05 and 110 has sloping end surfaces 117 (FIG. 11) and a recessed bottom end surface 118 for the flange portions 106 and 111. A pair of loop members 121 (FIG. 11) similar to the loop members 114, are embedded within each end portion of each beam 105 and 110 and project outwardly from the sloping end surface 117. The end portions of each beam 105 and 110 are supported by various combinations of precast concrete head support members 124, 126 and 128 each of which is constructed with four uniformly spaced vertical holes 131 (FIG. 11) within its center portion. As apparent from FIG. 10, the head support member 124 has a generally T-shaped configuration, and the head support 6 member 126 has an X-shaped configuration while the head support member 128 has an L-shaped configuration.

Each of the head support members includes a lower or bottom peripheral flange portion 134 which aligns with the flange portions 106 and III of the beams and and also abuts the adjacent recessed end surface 118 of the adjacent beams. Each of the head support members is mounted on a vertical precast concrete support post or column which is reinforced by a set of vertical reinforcing rods 142. The upper end portions of the reinforcing rods 142 project through the corresponding holes 131 within the corresponding head member and are also adapted to project above the head member into corresponding holes formed within the lower end portion of each column 140 mounted on top of the head member for supporting the next floor thereabove.

The head support members 124, I26 and 128 include a plurality of outwardly projecting block-like portions 148 each of which has embedded therein a U-shaped loop member 151 spaced above an L-shaped hook member 152. The outer end surface 153 of each portion 148 slopes on an angle which conforms to the angle of the outer end surface 1 17 of the adjacent beam 105 or 110.

The construction or erection of the floor or roof system shown in FIGS. 10-12, is commenced by positioning the posts or columns 140 on the base foundation or footer for the building. The precast head support members 124, I26 and 128 are mounted on the upper end surfaces of the columns 140 with the column reinforcing rods 142 extending through the corresponding holes 131 within the head support members. The precast and prestressed beams 105 and 110 are then placed in position with the lower loop member 121 at each end of each beam hooked onto the corresponding hook member 152 of the adjacent head support member. The upper loop member 121 overlaps the adjacent loop member 151, and a short rod segment (not shown) is inserted between the overlapping loop members to form a positive connection.

The precast concrete panels or slabs 90 are then placed in position with the ends of each slab resting on the underlying flange portions 106 of the beams 105. After a bay is completed with a series of adjacent slabs 90, a series of post-tension cables are fed through the laterally aligned tubes 101 within each set of slabs 90, and the cables are directed through or connected to the corresponding loop members 114 projecting upwardly from the beams 110 of each bay. The cables 160 are then tensioned. and a cement grout is pumped into the tubes 101 to form a bond between the cables 160 and the corresponding tubes 101 within each precast slab 90.

As apparent in FIG. 10, the upper surface of the head support members 124', I26 and 128 are substantially flush with or slightly above the top surfaces of the slabs 90, and the top surfaces of the beams 105 and 110 extend below the. top surfaces of the slabs 90 about 2 inches. Afterthe cables 160 are post-tensioned. a topping layer 162 of concrete is poured over the top of each beam 105 and 110. The topping concrete is also inserted into the mating cavities 103 of the adjacent slabs 90 and into the joints formed between the ends of each slab 90 and the adjacent support beams 105. The topping concrete layer 162 covering the beams 110 is efective to cover the post-tensioned cables 160 and the loop members II-l to form a bond between the cables I60 and the beams 110. Thus it is apparent that after a floor or roof is formed by the modular elements of the invention. the entire roof or floor structure acts as a monolithic continuous floor or roof structure which is prestressed in one direction and post-tensioned in the other direction. Thus the structure provides for a two way or X-Y distribution of the entire weight of the floor structure and the load supported by the floor structure so that the entire load is uniformly supported by the beams I and I10.

From the drawing and the above description. it is apparent that a floor or roof system constructed in accordance with the present invention. provides desirable features and advantages. The series of longitudinally spaced and laterally extending tubes within each of the precast reinforced beams 18 or 68 or slabs 90, provide for extending elongated reinforcing members or cables 60 or 160 laterally through the entire floor or roof structure. As a result. the longitudinally prestressed beams or slabs are reinforced or post-tensioned as a unit in a lateral direction by simply securing each tensioned cable 60 to each beam or slab with a cement or other bonding material which is pumped into the tube around the cable 60. Thus the weight of the floor or roof structure and the load supported by the structure is uniformly distributed both longitudinally of the beams and laterally across the beams. or in a two-way or X-Y direction so that the load of the floor or roof structure is uniformly supported by all of the bordering frame walls or columns of the building structure.

Furthermore. the prefabricated roof and flooring structure is adapted to be erected or assembled without the use of forms on site and thus results in more economical building construction. The use of the slab members 46 and 48 are particularly suited for constructing a floor or roof which has a lateral dimension different from even multiples of the width of each beam 18. That is. the length of the slab members 46 and 48 may be easily and conveniently changed to permit the floor structure shown in FIG. 3 to be used in a building structure of up to approximately 22 feet in length and width. On the other hand. if the building structure is designed to use of the flooring or roofing system of the invention. the beams 68 can be used in adjacent relation as shown in FIG. 9 without the use of the intermediate slab members 46 and 48. However. whichever modification is used. the spacing of the vertical walls which define the cavities 28 or 78 will remain uniform so that the load is uniformly distributed by the walls.

The embodiment shown in FIGS. I0 12 provides the additional feature of minimizing the time and cost of constructing or erecting a floor or roof structure by forming one or more bays each having a series of slabs 90 and a supporting framework formed by the beams 105 and 110 and the head members 124, I26 and 128. The set of slabs 90 within each bay are placed between the beams. and the casting of topping concrete 162 to embrace projecting reinforcing elements between the slabs and beams. provides for a monolithic continuous twoway roofing system. It is also apparent that the roofing system shown in FIGS. 1 8 is adapted for use with the frame system shown in FIGS. 10 12.

While the forms of floor structure herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of floor structure. and that changes may be made therein without departing from the scope and spirit of the invention. For example. it is apparent that the reinforcing rods 39 within each beam I8 or 68 may be replaced by prc-tensioned cables so that the beam is prestressed. or that the tubes 42 may be round instead of square or rectangular. It is also apparent that each of the beams 18 or 38 may have a relative width greater than that illustrated in the drawing and may include one or more longitudinally extending integral walls intermediate the side walls 20 or 69 and 72 and which cooperate with the intermediate walls 26 or 76 to define multiple laterally spaced rows of longitudinally spaced Cavities 28 or 78. The slabs shown in FIGS. 10 I2 illustrate this construction.

The invention having thus been described. the following is claimed:

1. In a prefabricated modular flooring system for a building structure. including a first set of parallel spaced elongated precast concrete beams disposed perpendicular to a second set of parallel spaced elongated precast concrete beams and cooperating to form a frame defining a bay. means for supporting the adjacent ends of said beams at the corners of said frame. a plurality of rectangular precast concrete floor slabs disposed in parallel horizontal relation within said frame and having opposite end portions mounted on said firrst set of beams for supporting one portion of the floor load by said first set of beams. each of said floor slabs including a plurality of laterally spaced longitudi nally extending walls projecting downwardly from an integrally connecting substantially flat horizontal upper wall. each of said floor slabs further including a plurality of longitudinally spaced and laterally extending transverse walls projecting downwardly from said upper wall and integrally connecting said upper and longitudinally extending walls to define a plurality of longitudinally and laterally spaced downwardly facing cavities providing the bottom of said floor slab with a waffle-type configuration. and a set of elongated reinforcing members extending longitudinally within each said floor slab through said longitudinally extending walls. the improvement comprising a set of longitudinally spaced tubes extending substantially horizontally through said transverse walls of each said floor slab. said tubes within one said floor slab being in substantial horizontal alignment with the corresponding said tubes within each horizontally adjacent said floor slab. and elongated flexible post-tension cable extending continuously through each set of horizontally aligned said tubes within said floor slabs, and means for securing said cables to said second set of beams and said floor slabs after said cables are tensioned to provide for supporting another portion of the floor load by said second sets of beams and there by produce a two-way distribution of the floor load to both said first and second sets of beams.

2. A modular flooring system as defined in claim 1 including a series of longitudinally disposed slab members positioned between adjacent said slabs, and each said slab member has a generally T-shaped cross-sectional configuration in a direction parallel to said elongated slabs.

3. A modular flooring system as defined in claim 1 wherein said second set of said beams each have outwardly projecting and longitudinally extending bottom flanges and a top surface disposed below the top surfaces of said slabs. said cables extend adjacent the top surfaces of said second set of beams. and means including a layer of concrete on the top surface of said second 9 set of beams for securing said cables to said second set of beams.

4. In a method of constructing a prefabricated modular flooring system for a building structure. including the steps of positioning a first set of parallel spaced elongated precast concrete beams perpendicular to a second set of parallel spaced elongated precast concrete beams to form a horizontal frame defining a bay, supporting the adjacent ends of said beams at the corners of said frame. positioning a plurality of rectangular precast concrete floor slabs in parallel horizontal relation within said frame with opposite end portions of said slabs mounted on said first set of beams for supporting a portion of the floor load by said first set of beams, forming each of said floor slabs with a plurality of laterally spaced longitudinally extending walls projecting downwardly from an integrally connecting substantially flat horizontal upper wall. forming each of said floor slabs with a plurality of longitudinally spaced and laterally extending transverse walls projecting downwardly from said upper wall and integrally connecting said upper and longitudinally extending walls to 10 define a plurality of longitudinally and laterally spaced downwardly facing cavities providing the bottom of said floor slab with a waffle-type configuration. and extending a set of elongated reinforcing members longitudinally within each said floor slab through said longitudinally extending walls. the improvement comprising the steps of extending a set of longitudinally spaced tubes substantially horizontally through said transverse walls of each said floor slab. locating said tubes within each floor slab in substantial horizontal alignment with the corresponding said tubes within each horizontally adjacent said floor slab. extending an elongated flexible post-tension cable continuously through each set of horizontally aligned said tubes within said floor slabs. and securing said cables to said second set of beams and said floor slabs after said cables are tensioned to provide for supporting another portion of the floor load by said second sets of beams and thereby produce a two-way distribution of the floor load to both said first and second sets of beams. 

1. In a prefabricated modular flooring system for a building structure, including a first set of parallel spaced elongated precast concrete beams disposed perpendicular to a second set of parallel spaced elongated precast concrete beams and cooperating to form a frame defining a bay, means for supporting the adjacent ends of said beams at the corners of said frame, a plurality of rectangular precast concrete floor slabs disposed in parallel horizontal relation within said frame and having opposite end portions mounted on said firrst set of beams for supporting one portion of the floor load by said first set of beams, each of said floor slabs including a plurality of laterally spaced longitudinally extending walls projecting downwardly from an integrally connecting substantially flat horizontal upper wall, each of said floor slabs further including a plurality of longitudinally spaced and laterally extending transverse walls projecting downwardly from said upper wall and integrally connecting said upper and longitudinally extending walls to define a plurality of longitudinally and laterally spaced downwardly facing cavities providing the bottom of said floor slab with a waffle-type configuration, and a set of elongated reinforcing members extending longitudinally within each said floor slab through said longitudinally extending walls, the improvement comprising a set of longitudinally spaced tubes extending substantially horizontally through said transverse walls of each said floor slab, said tubes within one said floor slab being in substantial horizontal alignment with the corresponding said tubes within each horizontally adjacent said floor slab, and elongated flexible post-tension cable extending continuously through each set of horizontally aligned said tubes within said floor slabs, and means for securing said cables to said second set of beams and said floor slabs after said cables are tensioned to provide for supporting another portion of the floor load by said second sets of beams and thereby produce a two-way distribution of the floor load to both said first and second sets of beams.
 2. A modular flooring system as defined in claim 1 including a series of longitudinally disposed slab members positioned between adjacent said slabs, and each said slab member has a generally T-shaped cross-sectional configuration in a direction parallel to said elongated slabs.
 3. A modular flooring system as defined in claim 1 wherein said second set of said beams each have outwardly projecting and longitudinally extending bottom flanges and a top surface disposed below the top surfaces of said slabs, said cables extend adjacent the top surfaces of said second set of beams, and means including a layer of concrete on the top surface of said second set of beams for securing said cables to said second set of beams.
 4. In a method of constructing a prefabricated modular flooring system for a building structure, including the steps of positioning a first set of parallel spaced elongated precast concrete beams perpendicular to a second set of parallel spaced elongated precast concrete beams to form a horizontal frame defining a bay, supporting the adjacent ends of said beams at the corners of said frame, positioning a plurality of rectangular precast concrete floor slabs in parallel horizontal relation within said frame with opposite end portions of said slabs mounted on said first set of beams for supporting a portion of the floor load by said first set of beams, forming each of said floor slabs with a plurality of laterally spaced longitudinally extending walls projecting downwardly from an integrally connecting substantially flat horizontal upper wall, forming each of said floor slabs with a plurality of longitudinally spaced and laterally extending transverse walls projecting downwardly from said upper wall and integrally connecting said upper and longitudinally extending walls to define a plurality of longitudinally and laterally spaced downwardly facing cavities providing the bottom of said floor slab with a waffle-type configuration, and extending a set of elongated reinforcing members longitudinally within each said floor slab through said longitudinally extending walls, the improvement comprising the steps of extending a set of longitudinally spaced tubes substantially horizontally through said transverse walls of each said floor slab, locating said tubes within each floor slab in substantial horizontal alignment with the corresponding said tubes witHin each horizontally adjacent said floor slab, extending an elongated flexible post-tension cable continuously through each set of horizontally aligned said tubes within said floor slabs, and securing said cables to said second set of beams and said floor slabs after said cables are tensioned to provide for supporting another portion of the floor load by said second sets of beams and thereby produce a two-way distribution of the floor load to both said first and second sets of beams. 